This paper studies amplify-and-forward (AF) relay strategies for two-way wireless relay networks consisting of two sources with a single antenna and multiple relays with a single antenna. The closed form of relay amplifying matrices (vectors) with the perfect cancelation of self-interference under both no-channel uncertainty and channel uncertainty is presented based on the minimum mean square error (MMSE) criterion. With the derived optimal relay amplifying matrices, the MMSE cost function behavior, the relay power usage, and the sum of the achievable rate are analyzed. Additionally, a filter for each destination will be provided to remove the influences of noises at the receivers.